In plastic pipe systems, connections between the various components must be sealed to prevent escape of fluids from the connections. The connections typically comprise an enlarged bell which receives a spigot. The spigot and bell can be formed as segments of pipe lengths or connecting members, such as elbows, T's, etc. In this application, the terms “fitting” and “pipe” are intended to include both pipe lengths and connecting members.
The seal between the bell and spigot is conventionally provided by a gasket mounted in one of the components of the connection and sealingly and resiliently engaging the other component. Most often, the seal is mounted in the bell and is engaged and deformed by the spigot such that a tight interference fit is formed to prevent the escape of fluid.
Gaskets formed exclusively of elastomeric material, such as natural rubber, are disadvantageous since they can be displaced from their intended position so as not to provide an adequate seal. For example, such gaskets may be pushed from their intended position during insertion of the spigot within the bell, which is know as “fishmouthing”.
Gaskets reinforced with metal bands can be deformed and the metal can corrode causing the gaskets to leak. Moreover, when such gaskets are made an integral segment of the pipe spigot, deformation or corrosion of the metal band can cause the entire pipe section to leak.
Gaskets reinforced with plastic locking rings have been increasingly used. Such gaskets are described in U.S. Pat. No. 4,343,480 to Vassallo and U.S. Pat. No. 4,579,354 to Vassallo and Valls, which are hereby incorporated by reference in their entirety. Although such systems have the advantage of reducing the amount of elastomeric material required to prevent tearing of the gasket upon making up of the joint and to discourage blow out at operating pressures, a gap normally results between the forward wall of the elastomeric gasket and the internal surface of the bent retaining wall of the hub of the pipe or fitting. Thus, the final dimensions of the bent retaining wall depends entirely on the steel bending die, which results in non-uniform retainer walls.